JP2988094B2 - Ringing choke converter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a ringing choke converter, and more particularly to a ringing choke converter having an output overcurrent protection function.

[0002]

2. Description of the Related Art FIG. 2 is a circuit diagram showing an example of a ringing choke converter having an output overcurrent protection function. The AC input Vi is converted into DC power by the rectifying / smoothing circuit 1 and converted into AC power again by the switching operation of the switching transistor 2. This AC power is applied to the primary winding 12 of the transformer 11, and AC power is induced in the secondary winding 13.

The AC power of the secondary winding 13 is converted into DC power again by the rectifying / smoothing circuit 15 and becomes a DC output V0 to serve as a power source for a load (not shown).

An overcurrent detecting circuit 18 is provided to detect an overcurrent of the output DC current, and the magnitude of the output DC current is detected by a current detecting resistor 19 and the detected voltage is supplied to the overcurrent detecting circuit 18 as a detection voltage. You are typing. The overcurrent detection circuit 18 compares the detected voltage with a predetermined reference voltage, and when an output overcurrent is detected, the output becomes active.

The active output activates the converter stop circuit 6 and turns off the switching transistor 2, thereby stopping the operation of the converter and enabling output overcurrent protection.

The induced voltage of the base winding 14 of the transformer 11 is converted to a direct current by a rectifying / smoothing circuit 8 and input to a control circuit 7 for controlling the switching of the transistor 2.

The auxiliary winding 1 with respect to the base winding 14
6, the induced power of the auxiliary winding 16 is converted into a direct current by the rectifying and smoothing circuit 7, and is always supplied as an operation power supply of the overcurrent detection circuit 18. 3 to 5 are impedance circuits.

The overcurrent protection operation of the circuit shown in FIG. 2 is as follows. That is, a reference voltage is provided inside the overcurrent detection circuit 18, and the reference voltage is constantly compared with a voltage (a voltage across the resistor 19) corresponding to the output current.
When the output overcurrent state is detected, the output of the overcurrent detection circuit 18 becomes active.

The active signal is transmitted to the primary side by an element such as a photocoupler and is applied to the input of the converter stop circuit 6, and the converter stop circuit 6 operates. At this time, the output of the converter stop circuit 6 connected to the base of the switching transistor 2 falls to the low potential side of the input voltage, so that the base current does not flow into the switching transistor 2, the switching transistor 2 turns off, and the converter stops. I do.

By providing the converter stop circuit 6 with a latch function, the converter can be continuously stopped when an output abnormality is detected even once. Further, when the converter stop circuit 6 operates, the impedance circuit 3 is connected so that the output impedance becomes lower than the input impedance of the switching transistor 2.

Such a conventional overcurrent protection circuit for a ringing choke converter requires a power supply for driving the overcurrent detection circuit, and when the converter is operating normally, the overcurrent detection circuit 18 In addition, power loss occurs in the overcurrent detection resistor 19, and the efficiency of the converter decreases.

[0012]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a ringing choke converter that does not require a special power supply for an overcurrent detection circuit and does not cause power loss.

[0013]

According to the present invention, there is provided a transformer having a primary winding, a secondary winding, and a base winding, and switching means for controlling application of the primary winding of the transformer while switching DC power. A ringing choke converter that rectifies and smoothes AC power obtained in the secondary winding and converts it into output DC power, wherein a series circuit of a saturable reactor and a resistor connected in parallel to the base winding, A ringing choke converter comprising: a converter stop circuit that is started and controlled by a voltage at a connection point between a saturable reactor and a resistor, wherein the switching operation of the switching unit is stopped by starting the converter stop circuit. Is obtained.

[0014]

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a circuit diagram of one embodiment of the present invention.
2 are denoted by the same reference numerals. In the figure, a series circuit of a saturable reactor 9 and a resistor 10 is connected in parallel to a base winding 14 of a transformer 11 of a ringing choke converter, and a connection point between the saturable reactor 9 and the resistor 10 is connected to an input of a converter stop circuit 6. The output of the converter stop circuit 6 is connected to the base of the switching transistor 2.

Next, the overcurrent protection operation of the circuit of FIG. 1 will be described. The ringing choke converter performs duty control for input fluctuations and frequency control for load fluctuations. As the output current increases, the switching frequency decreases, so that the voltage-time product of each winding of the transformer 11 increases as the output current increases. I do. Therefore, the base winding 14 of the transformer 11 (voltage waveform is connected to FIG.
The amount of change in the magnetic flux density of the saturable reactor 9 having the BH characteristic as shown in FIG. 3B also increases as the output current increases.

The output becomes overloaded, and Bm ≦ (1 / NS) (NB / N1) Vi Ton = (1 / NS) (NB / N1) (V0 + VF + VL) Toff (N: the number of turns of the saturable reactor 9) , S: the effective area of the core of the saturable reactor 9, VF: the forward drop voltage of the secondary rectifier diode of the transformer 11, and VL: the secondary line drop voltage. From infinity to zero, the voltage of the base winding 14 appears across the resistor 10.

The converter stop circuit 6 is operated by this voltage, the output of the converter stop circuit 6 connected to the base of the switching transistor 2 falls to the low potential side of the input voltage, and the base current flows into the switching transistor 2. Disappears, the switching transistor 2 turns off, and the converter stops. By making the converter stop circuit 6 have a latch function, when an output abnormality is detected once, the converter can be stopped continuously.

FIGS. 3A and 3B are specific circuit examples of the converter stop circuit 6 of FIG. 1. In FIG. 3A, when an overcurrent is detected, the n-type FET is turned on, and the light emission side of the photothyristor emits light. Then, the converter is stopped by turning on the light receiving side of the photothyristor.

Regarding (b), by connecting the output of the overcurrent detection circuit directly to the gate of the thyristor, when the overcurrent is detected, the thyristor is turned on and the converter is stopped.

When the converter stop circuit 6 operates, an impedance circuit 3 is connected so that its output impedance becomes lower than the input impedance of the switching transistor 2. This impedance circuit 3 is composed of a diode or a resistor. FIG. 4 is a diagram illustrating an example of the impedance circuit 5.

FIG. 6 is a circuit diagram of another embodiment of the present invention, and the same parts as those in FIG. 1 are denoted by the same reference numerals. FIG.
In the circuit of the first embodiment, the converter stop circuit 6 is constituted by a photothyristor light-receiving unit 20 and its light-emitting unit 21 is used for the output of the overvoltage detection circuit on the secondary side of the converter. This is a circuit that enables output protection for both currents.

That is, a series circuit of the Zener diode 22 and the light emitting unit 21 is provided in parallel with the DC output unit, and when the overvoltage is applied, the Zener diode 22 is turned on to excite the light emitting unit 21 to excite the photothyristor. Is turned on.

[0024]

As described above, according to the present invention, an overcurrent detection circuit using a saturable reactor is provided in a base winding of a transformer, and an output overcurrent is detected by a voltage-time product of the base winding. This eliminates the need for a power supply for driving the overcurrent detection circuit, and has the effect of eliminating power consumption by the overcurrent protection circuit during normal operation.

Further, if a photothyristor light receiving section is used for the converter stop circuit and its light emitting section is used for the overvoltage detecting circuit, not only overcurrent but also overvoltage can be detected.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of an embodiment of the present invention.

FIG. 2 is a circuit configuration diagram of a conventional ringing choke converter.

FIG. 3 is a diagram showing a specific example of a converter stop circuit.

FIG. 4 is a diagram illustrating an example of an impedance circuit.

5A is a diagram showing an induced voltage waveform of a base winding 14 of a transformer 11, and FIG. 5B is a diagram showing a BH characteristic of a saturable reactor 9. FIG.

FIG. 6 is a circuit diagram of another embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Input rectification smoothing circuit 2 Switching transistor 3-5 Impedance circuit 6 Converter stop circuit 7 Control circuit 8 Rectification smoothing circuit 9 Saturable reactor 10 Resistance 11 Transformer 12 Primary winding 13 Secondary winding 14 Base winding 15 Output rectification smoothing circuit

Claims (2)

(57) [Claims] A transformer having a primary winding, a secondary winding, and a base winding; switching means for controlling application of the primary winding of the transformer while switching DC power; A ringing choke converter that rectifies and smoothes the obtained AC power and converts it into output DC power, a series circuit of a saturable reactor and a resistor connected in parallel to the base winding, and a saturable reactor and a resistor. And a converter stop circuit that is controlled to be started by a voltage at a connection point of the ringing choke converter, wherein the switching operation of the switching means is stopped by starting the converter stop circuit. 2. The converter stop circuit comprises a light receiving portion of a photothyristor in which the voltage is applied to a gate terminal, and the light emitting portion of the photothyristor constitutes an overvoltage detecting circuit for detecting an overvoltage state of the output DC power. 2. The ringing choke converter according to claim 1, wherein: